Conventional freight railroad cars in North America and other parts of the world typically include a car body and two spaced apart trucks. The car body or car body under frame typically includes two spaced apart center plates that respectively rest on and are rotatably or swivelly received by bolster bowls of the two trucks. The trucks rollingly support the car body along railroad tracks or rails. Each truck typically has a three piece truck configuration that includes two spaced apart parallel side frames and a bolster. The side frames extend in the same direction as the tracks or rails, and the bolster extends transversely or laterally to the tracks or rails. The bolster extends laterally through and between and is supported by the two spaced apart side frames. Each side frame typically defines a center opening and pedestal jaw openings on each side of the center opening. Each end of each bolster is typically supported by a spring group positioned in the center opening of the side frame and supported by the lower portion of the side frame that defines the center opening. Each truck also typically includes two axles that support the side frames, four wheels, and four roller bearing assemblies respectively mounted on the ends of the axles.
Each truck further includes a brake assembly that typically includes two brake beam assemblies (i.e., one associated with each wheel and axle assembly) that are connected to brake rigging. Each brake beam assembly is supported between the truck side frames to enable such brake beam assembly to be operated into and out of braking positions in relation to the respective wheel and axle assembly. Each brake beam assembly has two spaced apart brake shoe assemblies (i.e., one associated with each wheel of the respective wheel and axle assembly). Each brake shoe assembly includes a brake head attached to the brake beam, a brake shoe, and a removable brake shoe retaining key that attaches or connects the brake shoe to the brake head. The known brake heads, brake shoes, and brake shoe retaining keys are made in accordance with Association of American Railroad (“AAR”) specifications pertaining to those particular components. Brake shoes regularly wear out in service and are required to be replaced when worn to a specified extent.
Each brake shoe is detachably connected to the respective brake head by the brake shoe key. The brake shoe key is removed to enable that brake shoe to be replaced when worn or otherwise necessary. More specifically, the back of each brake shoe includes a center attaching lug that typically includes a steel strap that forms a part of the keyway into which the brake shoe key is inserted. The brake head typically includes brake head pads configured to be positioned on opposite sides of the center attaching lug of the brake shoe when the brake shoe is mounted to the brake head.
Two types of brake shoe keys have been employed in the North American railroad market. The first type of brake shoe key is the wedge type key that is formed with a decreasing taper from the head end toward the foot or leading end. The wedge type key is driven into a keyway provided by the interfitting parts of the brake head and brake shoe to attach the brake shoe to the brake head by a wedging effect. Such wedge type keys may become loosened and allow relative movement between the brake shoe and the brake head. This is more likely to occur when the wedge type key is formed from a malleable iron.
The second type of brake shoe key is the spring type key that is formed from spring steel. This type of brake shoe key is configured such that it is under tension when it connects the brake shoe to the brake head. More particularly, this spring type brake shoe key is formed from a steel strip that has a width that enables it to fit tightly into the keyway provided when the brake shoe is mounted on the brake head. The thickness of the steel strip is sufficient to provide the required sturdiness of the brake shoe key when under tension in the keyway and is no thicker than the depth of the keyway.
While these spring type brake shoe keys are reasonably effective, it has been found that the heads of certain spring type brake shoe keys tend to break off in certain circumstances. It is believed that these heads break off due to the relative vibration or movement of the brake heads relative to the relative vibration or movement of the brake shoes. It is believed that the vibration or movements of these attached parts relative to one another causes the head of the brake shoe key to undergo continuous or substantial upward and downward bending forces when the railroad car moves or rolls along the tracks or rails, and that the combination of these forces eventually leads to the weakening of the head and can eventually cause the head to break off. The weakened head of the brake shoe key can also break off when a pry bar is employed to move the brake shoe key out of its locking position by wedging the pry bar between the head of the brake shoe key and the brake head.
Several problems are caused or potentially caused when the head of a brake shoe key breaks off. One problem or potential problem is that when the head breaks off, the brake shoe can become loose relative to the brake head and move into a non-ideal position for engagement with the outer circumference of the wheel when the brakes are applied. Another problem or potential problem is that when the head breaks off, the brake shoe key can fall completely out of the keyway, which in turn causes the brake shoe to no longer be securely connected to the brake head (and possibly lost). This can also lead to the shoeless brake head contacting and potentially damaging the wheel during a brake application.
Another problem or potential problem arises for coal (or other material) carrying railroad cars that work with rotary dump systems where the railroad cars are turned upside-down to empty the coal (or other materials). In this case, gravity can cause a loose brake shoe key to become dislodged, which can cause the brake shoe key or the brake shoe to fall into the coal (or other material) deposit. This can create problems and expense for material handlers (such as coal power plant operators) in providing metal detectors to locate lost brake shoe keys or brake shoes in the coal deposit and for the removal of these brake shoe keys or brake shoes. This is especially true where these lost components represent potential damage to expensive equipment (such as coal pulverizing machinery).
Accordingly, there is a need in the railroad industry to solve these problems.